1. Field of the Invention
This invention relates to a method of manufacturing an angle-of-rotation sensor for detecting the angle of rotation of a shaft. This invention particularly relates to a method of manufacturing an angle-of-rotation sensor for detecting the angle of rotation of the crankshaft of an internal combustion engine of an automobile or other such vehicle.
2. Description of the Prior Art
Recently, electronic control technology for internal combustion engines has been making rapid progress. With respect to such electronic control, control timing is important and as such it is necessary to detect with precision piston crank angle positions for use as reference signals. Conventional types of angle-of-rotation sensors include, for example, the type disclosed in Japanese Laid-open Patent Publication No. 57(1982)-133311. In this conventional technology a rotating member is formed by stacking three disk-shaped magnets one on top of the other. Each of the magnets has magnetic poles formed contiguously around the periphery thereof, forming three arrays of magnetized zones.
However, because in this conventional type the rotating member is formed by the stacking of disk-shaped magnets, the rotating member becomes heavy, requiring that the diameter of the shaft be increased, with the result that other parts such as the bearings have had to be made large, so that overall the sensor becomes large and heavy, requiring a large space to house it in and causing a degradation in durability.
It is thereupon conceived that a magnetic member could be employed in place of the disk-shaped magnets, such as tubular magnetic ring formed of ferrite, for example, and a shaft arranged coaxially therein, and filling the space therebetween with resin. However, the brittle nature of ferrites is well known, in addition to which, when formed into a tubular shape, they are relatively weak to outward-acting tensile stress, and there is therefore a risk that if the tubular magnetic ring is filled rapidly with the resin, the said tensile stress would fracture or crack the magnetic ring. In addition, it is not necessarily easy to firmly fasten the magnetic ring to the shaft so that no slippage would occur therebetween.